Current sensors that are based on concentric-pipe geometry are generally known in the art. However, in a three-phase system or network such current sensors may have problems regarding the sensitivity or accuracy of the current sensor due to mutual coupling of alternating voltages provided between the three phases.
Techniques are known to reduce the mutual coupling between the current sensors in such a three-phase network or system. One technique for accomplishing this is to introduce magnetic insulation. Unfortunately, such magnetic insulation may introduce other problems in that the insulation may become saturated due to the strength of components of the magnetic field and, furthermore, such insulation may not be economical for some current sensing applications or may introduce additional size and bulk, especially due to the need for materials able to provide satisfactory insulation.
Another disadvantage encountered in known current sensor scan be the need for a relatively expensive current shunt which is meticulously designed for providing a highly accurate current measurement. For instance, use of such current shunt helps somewhat to reduce the size, weight, and expense of the current sensor by reducing the number of ampere-turns in the active part of the current sensor such as in a zero-flux detection technique. However, even the use of an accurate current shunt typically introduces some expense due to the current sensor materials, such as low temperature coefficient materials, the large number of coil "turns" in the sensing and feedback coils on the current shunt, as well as the manufacturing care required to fabricate the current sensor. Thus, a need exists for a current sensor and method for overcoming these problems.
Moreover, since current sensors typically have associated circuitry, such as signal conditioning circuits, signal processing circuits, control circuits and the like, it is also desirable for the current sensor to have a self-powering capability which allows for electrically powering such associated circuits in a manner which avoids the need for any current shunt and which is essentially independent or separate from any current measurement or current sensing operation being performed in the current sensor. This is particularly desirable since the respective design and accuracy requirements of any current shunt and associated transformer elements, such as the transformer core and coil, that are employed both for current sensing and for self-powering, are typically much more demanding or restrictive than would be the respective design and accuracy requirements of transformer elements which are exclusively dedicated for self-powering. For example, this would advantageously allow for further reducing the size, weight, and cost of the current sensor due to the greater flexibility of design and lower expense of transformer elements which are exclusively dedicated for self-powering, as compared to a current shunt and transformer elements which must also provide highly accurate current measurements. Moreover, high-power circuit breaker applications generally require current sensors having a high dynamic range and accuracy while maintaining a relatively low cost and size.